Specific-heat study of nanocrystalline palladium.

We have performed measurements of the low-temperature specific heat for T =0.7—20 K and magnet0 ic susceptibility for T = 1.8—300 K of Pd nanocrystals with average particle size 84 A. An enhancement 0 of the specific heat is observed at temperatures T & 3.5 K for 84-A Pd nanocrystals. This enhancement is primarily related to the softening of and the size effect on the phonons. The temperature coefficient of specific heat y decreases to a lower value as compared to that of bulk Pd. An estimated surface coefficient of specific heat y, is about 30% that of the bulk. This is also refiected in a reduction of the magnetic susceptibility of the Pd nanocrystals. The peak of the magnetic susceptibility observed at —80 K in bulk Pd is not observed in the nanocrystals; this could be due to a change of the energy band structure in the Pd nanocrystals.